Method of operating reverberatory furnaces and smelting ores therein



Nov. 24, 1931. E. w. DAVIS 1,833,321

METHOD OF OPERATING REVERBERATORY FURNACES AND SMELTING ORES THEREIN Original Filed Nov. 23. 1929 4 Sheets-Sheet l INVENTOR Edward 11701:

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ATTORNE NOV. 24, 1931. w DAVIS 1,833,321

METHOD OF OPERATING REVERBERATORYFURNACES AND SMELTING ORES THEREIN Original Filed Nov. 23. 1929 -4 Sheets-Sheet 2 INVENTOR LZ O MQ ATTOR EY 5 E. W. DAVIS Nov. 24, 1931.

4 Sheets-Sheet 3 Original Filed NOV. 25, 1929 INVENTOR [Zia/0rd Wflaz/z's Nov. 24, 1931. I E, w, DAVIS 1,833,321

METHOD OF OPERATING \REVERBE'RATORY! FURNACES AND SMELTING ORES THEREiN Original F iled- Nov. 25. 1929 4 Shee'ts-Sheet 4 7 INVENTOR [IQ/am fi-"Jams Patented Nov. 24, 1931 UNITED STATES EDWARD w. DAVIS,

PATENT OFFICE OF MINNEAPOLIS, MINNESOTA, ASSIGNOR TO DAVIS STEEL PROCESS CORPORATION, A CORPORATION OF DELAWARE METHOD OF OPERATING REVERBERATORY FURNACES. AN'D SMEITING ORES THEREIN Application filed November 23, 1929, Serial No. 409,225. Renewed July 18, 1931.

This invention relates to methods of smelting ores, concentrates and similar materials, and in particular to such methods carried out in furnaces of the reverberatory type.

According to certain methods heretofore employed in smelting finely-divided ores, the ore has been fed through openings either in the roof or side walls so as to build up piles of ore presenting extended surfaces in a posi tion to be rapidly acted upon by the smelting flame passing through the furnace. Various means have been employed or proposed for feeding the ore to the furnace, such as hoppers adapted to feed by gravity, and screw conveyors and plungers so positioned as to force the charge into the furnace, through spaced openings in the side walls, underneath an back of the previous charge.

\Vhile certain of the earlier proposals have had as an object the gradual and'uniform heating of the charge from the smelting face thereof inwardly and the feeding of fresh ore to the charge at a point remote from the smelting face and with minimum disturbance thereof, no prior worker, insofar as I am aware, has disclosed a means capable of being so operated as to attain this object; nor has any prior disclosure, with which I am familiar, indicated any appreciation of certain important factors entering into the successful operation of such smelting methods. In particular, insuflicient attention apparently has been given to the fact that in reverberatory smelting operations of this type the temperature conditions obtalning at various portions of the smelting face.

of the charge vary considerably, with the result that the charge smelts down much more rapidly in certain places than in others, and if this is not taken into account disturbances of the smelting face occur.

The present invention comprises means for feeding the charge in a layer of substantially uniform thickness through an elongated opening along one or both sides of the furnace, so as to present an inclined body of charge within the furnace, and for supplying fresh materials to the charge and advancing the body of charge gradually as the face thereof is smelted, without causing material disturbance of the smelting face. The smelting face of the charge within the furnace will be coincident with an inclined plane making an angle, with the horizontal, less than the angle of repose of the charge material. By maintaining an essentially stable body of charge with a substantially unbroken smelting surface, the exposure of fresh, relatively cold ore to the action of the smelting flame is avoided and the danger of any unreduced ore entering the slag or metal bath is reduced to a mlnlmum.

The invention in its broad aspects relates to a method for so feeding the charge, that for carrying out the invention, means are provided for confining the charge at the charging-opening, and for some distance in point of travel anterior thereto, in a columnar ody which at the charging opening substantially conforms in cross-section to that of the charging opening, and is confined and supported on its under side by a concave supporting member adapted to move beneath the superimposed body of charge material substantially in the arc of a circle, the center of.

which is determined in a manner hereinafter described. Through frictional contact with the superimposed material, each particle lying in any radius drawn from the center of said circle to said concave member is thereby caused to move in a circular path about such center while maintaining its relative position in the body of the charge material substantially unchanged with respect to adjacent particles of the charge. 7

While the present invention is of general application in the treatment of finely-divided ores and similar metalliferous materials, it is particularly applicable in the reduction of finely-divided iron ores and iron-contain ing materials with direct production therefrom of fluid iron or steel, and insofar as the reduction of iron from its ores and iron-containing materials is described and claimed herein, the present invention is to be regarded as an improvement upon. the process described in my co-pending application Serial No. 293,491, filed July 17, 1928.

The invention will be described in further detail by reference to the accompanying drawings in which:

Fig. I is a vertical cross-sectional view taken midway of the length of the furnace and showing the relation of the feeder mechanism tothe structural features of the furnace;

Fig. II is a vertical cross-sectional view through one of the feeders showing the details of a preferred form of feeder mechanism;

Fig. III is a longitudinal cross-sectional view through the center of the furnace showing the settling pocket located at one end of the hearth; i

Fig. IV is a side elevation showing one feeder in position;

Fig. V is a top planview of the furnace and feeder mechanism; and Fig. VI is a cross-sectional view through a cylinder showing graphically the paths taken during rotation'thereof by particles of a comminuted material disposed therein.

Referring to the drawings (Figures I and II) 10 represents the hearth of a reverbera tory furnace, 12 a suspended roof therefor, and 14 represents generally a preferred form of feeder. mechanism associated therewith. In the construction shown, the furnace is devoid of side walls as ordinarily understood, their place being taken in operation by the slowly advancing body of charge materials. The roof 12 is brought closer to the hearth than has heretofore been the case in reverberatory practice and is of a suspended arch construction, which may, for example, comprise a pair of skew-backs 16 extending longitudinally of and at each side of the roof, each being suspended by a plurality of hanger arms 18 from I beams 20 which in turn are supported at their ends by upright members 22. The hanger arms 18 are pivoted as at 24. Tie rods 26, secured to the hanger arms as at 28, are carried through openings in blocks 30 carried by the I beams 20. A pull is applied through the tie rods 26 against the lower ends of the hanger arms by means of the coil springs 32, thereby tending to move the hanger arms about their pivots and to press the skew-backs toward one another, and to take care of contraction and expansion of the arch. The roof preferably extends some distance beyond the sides of the hearth over a shelf 34 extending along the side of the hearth.

The feeder mechanism, according to a form which has proved satisfactory in practice, consists of upright supporting members 22 and 36 joined by bracing members38 and 40. Carried by the member 38 are links 42 and 44 pivoted at their lower ends respectively at 46 and 48 and at their upper ends at 50 and 52 to a feeder plate 54.

A reciprocating movement is imparted to the feeder plate 54 by means of a hydraulic cylinder 56, connected through the bell crank levers 58 and 60 and the link 62 with the link 42. Disposed above the feeder plate is a hopper 64 located in such a way that the entire bottom of the hopper is formed by the feeder plate 54. In the drawing this hopper is shown as provided with a divider plate 66 partitioning the hopper into a large compartment 68 and a relatively small compartment 70. The divider plate may be omitted, if desired. The bell crank levers and connecting links are so constructed as to produce only a short back and forth movement, say from to 1", depending upon the kind of charge materials being fed and the depth of the layer of charge being advanced.

It is to be understood that, although a feeder mechanism of the lever type, reciprocating in action, is described in detail in the preceding pages of this specification, the invention is not limited to this particular mechanism as a means of attaining the desired result. The essential feature of the invention is the uniform, progressive, movement of the body of charge downwardly and forwardly into the furnace in such a manner as will result in an undisturbed smelting face within the furnace always lying in an inclined plane making an angle with the horizontal less than that of repose of the materials of the charge under'the temperature conditions obtaining. The use of any mechanism which would so impart a movement to the curved feeder plate as to attain this desired result is to be considered as within the scope of this invention.

In Fig. III is shown a novel feature of furnace construction in the form of a settling pocket 76 located at one end ofthe hearth. This settling pocket, set into the hearth floor,

affords a reservoir for the accumulation of the fluid products of the smelting operation. It is so arranged in relation to the rest of the hearth that the fluid materials flowing 'down the banks of charge material collect for drawing off said fluid products continuously or intermittently as may be desired. By the incorporation of this novel feature, as an integral part of the general furnace construction, there is avoided any appreciable accumulation of fluid material, in the form of a slag and metal bath, on the fioor of the hearth proper. It is thereby made possible to operate with a maximum area of smelting surface and thus impart a greater smelting capacity to the furnace, by increasing the area of the smelting faces exposed, at the portion thereof lying in the zone of most rapid smelting, to the action of smelting flame.

In operation the hopper is preferably kept sufliciently filled to insure that the ore body seals tightly against the roof of the furnace.

The skew-back members are preferably water cooled so as better to protect the brickwork from contact with the materials of the charge. When iron ores are being reduced,

it is particularly desirable to prevent contact of the iron oxide of the charge with the brickwork of the furnace, since otherwise there is a tendency for the oxide to attack the brickwork at the temperatures of operation.

With the feeder means above described, it is possible to feed the ore gradually forward in such a way that each particle, in travelling in the confined path defined by the feeder plate 54 on the lower side and the skew-back 16 on the upper side, moves along a line substantially constituting the arc of a circle concentric with, and, for all particles except those resting directly upon the feeder plate, of lesser diameter than that defined bythe feeder plate. This is il-' lustrated by the dotted lines a in Figures I and II, which dotted lines represent paths of travel of particles ofcharge at their respective indicated distances from the feeder plate from the time they pass the throat defined by the skew-back on the one side and the feeder plate on the other until they are brought to the smelting face. That this is so will appear obvious by reference to Fig. VI in which 6 represents a cylinder and c a body of comminuted material confined to the cross-hatched portion of the cross-sectional. area of the cylinder. Let us assume that the; cylinder and its contents have been rotated so that the face of the bodyof comminuted material indicated as m-y has been moved from the position indicated by the dotted lines a:g It will now be seen that any particles adjacent the periphery of the cylinder have moved through the distance y y whereas the movement in the particles at a; is nil; also, that the relative distances travelled. or the relative rates of travel, of particles spaced at any distance from the center w will be proportional to their distances from such center.

' The heat conditions obtaining in the furnace are normally such that the greatest amount of heat is applied to the lower portions of the inclined bank of charge material, and, therefore, the more rapid smelting of the charge materials in this portion of the smelting face needs to, be compensated for by bringing the charge materials to the zone of more rapid smelting at a proportionally greater rate. At the same time the particles of charge should, when brought to the smelting face, remain quiescent until smelted and fused. Therefore, it follows that the inclination of the smelting face must always be less than the angle of repose of the particular charge materials being treated. From the above it will be seenthat, once the difference in rate of smelting in different zones on the face of the charge have been determined for given heat conditions and the angle of re-' pose ofthe charge material ascertained, the

relative rate at which the materials at the lower edge or toe of the smelting face must be fed as compared with that at the upper edge is capable of accurate ascertainment. It thenbecomes necessary only to so locate and proportion the feeder plate that it shall describe the arc of a circle, the center of which is 10- cated at such distance from and in such relation to the feeder plate that the distance from the upper edge of the smelting face to such center and the distance from the feeder plate to such center, measured on a radius drawn from such center to the feeder plate and intersecting the upper edge of the smelting face, bear a relation proportionate to the relative rates of feed desired at the upper edge and the lower edge or toe of the smelting face. In this way there is prevented any un- I desired downward movement of the materials at the face of the charge before they are completely smelted, and thus there is avoided the exposure of raw unreduced charge materials to the smelting flame, or a mixing of such unreduced materials with the fluid metal and slag collected in the hearth.

It will be understood that a change in the rate of heat input or the distribution of the 'tive rate of feed at the toe of the smelting face as compared with the rate of feed at the upper edge thereof. When the change in the heat input or heat distribution is too great, redesigning or relocation of the feeder plate may be required.

In operating with iron ores, such as Mesabi hematites and magnetites, in the form of a mixed charge of ore, carbon and slag-forming materials, previously crushed or otherwise reduced to finely divided form (ore reduced to 150 mesh, flux forming materials to 4 mesh and coal to 6 mesh), I find that the angle ofrepose may be taken as approximately 37 to the horizontal.

. The furnace illustratedin part in Fig. II was designed with a view to giving a rate of feed such that the slope of the smelting face of the charge would be slightly less than that of the angle of repose, or that represented by the dotted line (Z. In actual operation on a charge consisting of ore, coal and limestone in the proportions of 100 parts of ore, 10 parts of limestone and coal calculated to equal 80'per cent of the iron present, with 'l'urnacetemperatures of approximately 1575 C. and a feed rate represented by reciprocating the feeder plate inch at the rate of one complete stroke every two minutes, the smelting face assumed the inclination illustrated in Fig. II.

It will be observedthat the operation of the feeder is such that if stratification of the materials of the charge is desired,this may be accomplished. By employing one or more divider plates such as shown in Fig. I different materials may be introduced to the several compartments of the hopper. These materials in feeding downwardly into the furnace will be maintained in clearly defined strata. to partially or completely surround the ore charge with a layer of carbon. If, so, coal or other suitable carbonaceous material may be introduced to the compartment 70, with ore introduced either alone or mixed with suitable amounts of reducing and fluxing materials introduced to. thecompartment 68. Spaced end plates 72 and 74 may also be introduced into the hopper and the spaces between the same and the ends filled with coal or other carbonaceous material. As the materials are fed downwardly and into the furnace the body or ore issuing from the compartment 68 will remain surrounded on the bottom and sides by the layer of carbon.

' The carbon entering the furnace beneath the ore charge, if originally in the form of coal, may become coked and then passed downwardly into the metal or slag bath into which it may be absorbed with resulting reduction or carburization of the metal, if the process is one of reducing iron, or it may function as a deoxidizing agent for the bath if non-ferrous materials are being treated.

In reducing iron ores according to the process described in my co-pending applica tion above mentioned, it will generally be advisable to feed the ore-coal-fiux charge without stratification, or merely with a layer of carbon interposed between the charge and the feeder plate on the one hand and betweenthe charge and the end walls on the other, thus As an example, it may be desirable serving to protect the brickwork of the shelf 34 and the end walls against the scorifying action of the iron oxide of the charge.

The present invention is particularly applicable in carrying out the process of my co-pending application above mention, since it provides a relatively simple and practical way to bring the charge gradually and uniformly to the reducing and carburizing stages and makes possible the carrying out of such operations under conditions such that the difierential in the rates of combustion of the carbon of the charge and carburization of the metal are established and maintained.

Wherever I have used the term angle of repose in this application, I am to be understood as meaning specifically that angle at which the material will lie quiescent in the ore bank under the conditions obtaining in the furnace. This angle changes substantially with different materials and with different mixtures of the same materials. In some cases a substantial crust develops at the smelting surface which makes possible the maintenance of a steeper quiescent slope on the smelting surfaces than would be possible with such materials if no crust was formed. As above stated, it is essential that the ore particles at the smelting surface shall remain quiescent throughout the smelting operation irrespective of whether any crust is formed,

The improved apparatus disclosed therein and referred to and described in the present invention forms the subject matter 0 my co-pending application Serial No. 497,997 filed November 25, 1930.

I claim:

1. The method of operating a reverberatory smelting furnace which comprises establishing a sloping body of charge adjacent the side of the furnace with the surface of the charge that is exposed to the atmosphere in the furnace inclined to the horizontal at an angle less than that of repose of the materials of the charge, maintaining a smelting temperature within the furnace, thereby causing smelting of the charge progressively inwardly from the exposed surface thereof, and advancing the" sloping body of charge and supplying fresh charge materials thereto at a point posterior to the smelting face at such rates in the various portions of the body of the charge that the smelting surface is kept free from disturhances and inclined at an angle to the horizontal less than that of repose of the materials of the charge.

2. The method of smelting iron ores in a furnace of the reverberatory type which comprises forming a charge of ore, carbon and slag-forming constituents, establishing a sloping body-of the charge adjacent the side of the furnace with the surface of the charge that is exposed to the atmosphere in the furnace inclined to the horizontal at an angle less than that of repose of the materials of the charge, maintaining a smelting temperature within the furnace to smelt the charge progressively inwardly from the exposed surface and to carburize and melt the reduced metal, flowing the molten metal and slag as formed away from the smelting face,

4 and advancing the sloping body of charge and supplying fresh charge materials thereto at a point posterior to the smelting face at such rates in the various portions of the body of the charge that the smelting surface is kept free from disturbances and inclined at an angle to the horizontal less than thatof repose of the materials of the charge.

3. The method of operating a reverberatory smelting furnace which comprises estab- V lishing a sloping body of charge adjacent the side of the furnace with the surface of the charge that is exposed .to the atmosphere in the furnace inclined to the horizontal at an angle less than that of repose of the materials of the charge, maintaining a smelting temperature within the furnace, thereby causing smelting of the charge progressively inwardly from the exposed surface thereof, and advancing the sloping body of charge and supplying fresh charge materials thereto in stratified form at a point posterior to the smelting face and at such rates. in the vari November, 1929. a

- EDWARD W. DAVIS. 

